The present invention relates to an improved machine for forming thin, spiral grooves in the inner surface of a metal pipe.
The heat transmission pipes of an air conditioner, for instance, have inner surfaces which are grooved. In a conventional method of forming grooves in the inner surface of a metal pipe, a predetermined grooving plug is inserted and held in a metal pipe such as a copper pipe in such a manner that its axial position is constant. The metal pipe, while being moved in the axial direction, is pressed by a plurality of rolls which rotate planetarily around the part of the metal pipe where the grooving plug is positioned.
For implementation of this method, a machine for forming grooves in the inner surface of a metal pipe (hereinafter referred to merely as "a grooving machine" when applicable) can be readily constructed by combining an ordinary drawing machine with a draw bench, a bull block or a continuous drawing bench. However, in such a machine, when the metal pipe is moved, the stress caused in the metal pipe by friction between the metal pipe and the rolls is high and therefore the speed of processing the metal pipe may be limited because of the tensile strength of the metal pipe. Because of the limitation in processing speed, the application of this method to a metal pipe having a small wall thickness and small diameter is undesirable because the speed of processing such a metal pipe is unavoidably low.